1. Field of the Invention
The present invention relates to a support for a lithographic printing plate and a presensitized plate. More particularly, the present invention relates to a support for a lithographic printing plate achieving both high scum resistance and long press life when processed into a lithographic printing plate, a presensitized plate using the support for a lithographic printing plate.
2. Description of the Related Art
It has been known that a hydrophilic treatment represented by a silicate treatment is performed on the surface of a lithographic printing plate after an anodizing treatment was performed thereon in order to enhance the development property of a presensitized plate. If a hydrophilic treatment is performed on the surface of a support for a lithographic printing plate, scum resistance is improved since ink which is hydrophobic is hardly adhered to non-image areas of a lithographic printing plate at the time of printing.
However, if a hydrophilic treatment is performed on the surface of a support for a lithographic printing plate, there is a case that an adhesion between an image recording layer which is hydrophobic and a support deteriorates in a presensitized plate, and press life deteriorates when processed into a lithographic printing plate.
Accordingly, a presensitized plate excellent in both scum resistance and press life when processed into a lithographic printing plate is expected.
As a countermeasure thereto, a method for improving press life is proposed by further performing a treatment on the surface of a support for a lithographic printing plate with an aqueous solution containing heavy metals such as cobalt and zirconium after a hydrophilic treatment is performed thereon (JP 7-314937 A (the term “JP XX-XXXXXX A” as used herein means an “unexamined published Japanese patent application”) or the like).
With the above method, although press life is improved, scum resistance deteriorates.
In the meanwhile, scum is likely to occur during printing with a presensitized plate having an image recording layer containing an infrared absorbent such as a so-called thermal positive type image recording layer in which an infrared absorbent existent in a photosensitive layer manifests its photothermal conversion action and an exposure generates heat, whereby an exposed area in the photosensitive layer becomes alkali-soluble to form a positive image, and a so-called thermal negative type image recording layer in which its exposure-caused heat allows a radical generator or an acid forming agent to generate a radical or an acid, by which a radical polymerization reaction or an acid crosslinking reaction is accelerated and an image recording layer becomes insoluble to form a negative type image. Taken up as one of the reasons why scum is generated is that since infrared absorbents used in these image recording layers are compounds having a relative higher molecular weight, they are hardly dissolved in a developer and are likely to be adsorbed to the surface of non-image areas on a lithographic printing plate at the time of development.
Conventionally with a presensitized plate having an image recording layer containing the infrared absorbent like this, it is particularly difficult to materialize the production of a presensitized plate excellent in both the above scum resistance and press life.
In addition, in JP 10-171104 A, methods for improving scum resistance after stopping printing for a while, press life and the like are proposed (i) by performing a hydrophilic treatment with a metal silicate aqueous solution in which the mol ratio of SiO2/M2O (M represents an alkali metal) is 0.3 to 4.0 and the concentration of an alkali metal silicate is 0.05 to 0.5 wt % before or after a treatment is performed with a carboxylate aqueous solution or (ii) by performing a hydrophilic treatment with a hydrophilic high-molecular weight compound aqueous solution after a treatment is performed with a carboxylate aqueous solution.
The methods as described in the above publication are, however, intended to improve scum resistance after stopping printing for a while, press life and the like to a so-called conventional positive type image recording layer and it can not be said that the methods are not excellent in achieving both scum resistance and press life relative to an image recording layer containing an infrared absorbent in which scum is likely to occur during printing.